This invention relates generally to shaft-mounted bearings and, more particularly, to hexagonal and square bore bearings for mounting on hexagonal and square shafts, respectively.
Hexagonal bore and square bore bearings are commonly used in agricultural machinery, such as for example disc harrows. The hexagonal or square bore within the inner ring of such bearings is positioned over a mid-portion of a complementary hexagonal or square shaft to prevent motion of the inner ring relative to the shaft. Such bearings are also used in applications outside the field of agricultural machinery to mount a rotating hexagonal or square shaft.
Typically, bearings of this type that are manufactured for use in agricultural machinery have a dimensional tolerance of approximately 0.005 inch at the hexagonal or square bore. Variations in the dimensions can be attributed to distortions caused by broaching the bores in the soft state before hardening or to heat treat growth after broaching. Also, broach tool tolerances, tool wear, and gaging errors may add to tolerance build up.
Current practice is to have full interchangeability of shafts and bearings; that is, all bearings are made with a bore larger than the maximum size of the shaft to be fitted. The shafting is generally cold drawn and has an associated dimensional tolerance of approximately 0.004 inch. Thus, if a particular shaft is 0.004 inch under nominal size and a bearing bore is 0.005 inch over nominal size, the resulting maximum clearance would be 0.009 inch. The average clearance would be 0.0045 inch.
This manufacturing clearance may adversely affect bearing life, noise, shaft fretting, and maximum rotational speed of the bearing. Additional clearance may result from wear of the shaft or the bore of the bearing during use, increasing the adverse affects.
To manufacture the bore or the shaft to tighter dimensional tolerances by grinding rather than standard machining technique would result in substantial increased cost. Other means for preventing motion of the inner ring relative to the shaft, such as an eccentric collar, cam lock, or set screw on a collar, also result in increased cost and require additional axial length. In addition, such alternative retention devices may loosen during use and allow the inner ring to rotate with the shaft.
The foregoing illustrates limitations known to exist in present bearings for mounting on multi-sided shafts. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one of more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.